The shear stress of flowing blood on artery walls and the surfaces of prosthetic devices has a significant influence on the integrity of blood components, the coagulation of blood and formation of thrombi, the production of biochemicals by endothelial cells, the regulation of arterial lumen dimension and the permeability of artery walls to macromolecules and other solutes. In addition, wall shear stress is believed by any to play a role in the pathogenesis of atherosclerosis, an arterial disease which is localized at branch points and bends in arteries. Until recently, knowledge of wall shear stress magnitude and spatial variation in the circulation came primarily from in vitro experiments in rigid models of isolated arterial segments employing Newtonian blood analog fluids. The proposed research investigates the importance of arterial wall elasticity, non-Newtonian blood rheology and the interaction of local and systemic arterial properties in determining the magnitude and distribution of wall shear stress in the cardiovascular system. In the proposed research the following studies will be conducted: 1. Wall shear stress will be measured in dog aortas under normal conditions and altered conditions induced by vasoactive drugs. A hot film anemometer probe designed especially for flush mounting on artery walls will be utilized. 2. Wall shear stress will be measured in elastic models of curved and branched arteries using non-Newtonian blood analog fluids and blood under_physiological flow conditions. Hydraulic impedance elements in a mock circulatory loop will be used to simulate the hemodynamic environment of several arterial segments. 3. Computer simulations of blood flow in arteries which take into account physiologic radial motion of the vessel wall and non- Newtonian blood rheology will be developed. Radial wall motion will be coupled to the pressure pulse through circulatory impedance data, and a power law rheological equation-will model blood. Extensive comparisons between computer simulations and experiments will be made.